Document U.S. Pat. No. 5,394,098 describes an example of such a device used for testing optoelectronic components, using an optical source consisting of a laser. More precisely, electric fields are measured in the optoelectronic components by means of a layer of material constituting an optically active medium covering at least part of the component that it is desired to test.
In the present document, the expression “optically active medium” is understood to mean a medium having electrooptic properties and more particularly a medium having a linear electrooptic effect (also called the Pockels effect), or a quadratic electrooptic effect, the manifestation threshold of which is however higher than in the linear case, while still remaining compatible with the use of short-pulse power lasers.
This type of device does however have the drawback of allowing measurements only at a signal sampling frequency fa above the cutoff frequency fc. This type of device cannot be used in particular for detection of electric fields within the volume of biological media, since the variations in refractive index that are due to electric fields in biological systems essentially take place at frequencies below 1 kHz, whereas the frequency fc must be a few kHz in order to eliminate external (thermal, mechanical, acoustic, etc.) noise.
It is an object of the present invention in particular to alleviate this drawback.